50 THE NATURE AND WORE OF PLANTS 



Measure the distance between the marks daily for a 

 week. In what part of the root does most of the 

 growth take place ? Compare with the growth of 

 roots ( 54), leaves ( 113), and stems ( 144-151). 



55. Absorbing and fixing organs of the lower 

 plants. Roots represent the most highly perfected 

 organs for the fixation of the plant in its position 

 and the absorption of food. In the lower forms, 

 incapable of building such complex organs, these 

 functions must be carried on by simpler structures, 

 which perhaps must take other and additional 

 work. 



56. Absorbing and fixing organs of the ferns, 

 mosses, and liverworts. Among the ferns, mosses, 

 and liverworts absorption and fixation are carried 

 on chiefly by means of large tubes termed rhizoids, 

 which resemble root-hairs except in size and heavi- 

 ness of the walls, although rootlike organs are pres- 

 ent in some species. Some of these forms are very 

 much like the higher plants, in which instance the 

 large rhizoids are attached to the underground parts 

 like root-hairs. In other instances the plant is in 

 the form of a leaflike body, which lies on the surface 

 of the ground. The rhizoids spring directly from 



